Morbidity and mortality from pediatric asthma have been increasing in developed countries over the past three decades, making asthma the most common chronic disease of children. A joint session at the American Thoracic Society meeting in May 2000 was titled "Childhood Asthma: Is Change in Lifestyle the Key"? During this session, the hypothesis was advanced that a lack of physical exercise and higher levels of childhood obesity may be contributing to an increased incidence of asthma among US children. We have a large population-based multi-ethnic cohort of school children (n=826) from the Detroit area for whom, using dual-energy x-ray absorptiometry, precise measurements of whole body bone mass, and soft tissue composition were collected along with height and weight measurements in 1992- 1993, when the children were nine years old. Detailed data on physical activity, collected with consultation with an exercise physiologist, and prevalent asthma diagnosis and symptoms, collected under the direction of a respiratory disease/pediatric epidemiologist and a pediatric allergist, were obtained at the same time. The physician diagnosis of pediatric asthma will be assessed for relationships with the potential risk factors body mass index, percent fat and lean tissue, obesity, and physical activity. Our approach, optimizing the use of historical baseline data, is a methodologically sound and cost-effective means of investigating the relationship of childhood lifestyle and physical characteristics to prevalent asthma.